Unwritten and Undone: How Brexit Is Quietly Redrawing Britain's Constitutional Landscape

Britain has always governed itself through constitutional convention rather than codified law. No single document defines the limits of executive power, the independence of the judiciary, or the supremacy of Parliament. For decades, membership of the European Union provided an external framework that, whatever its critics argued, imposed a degree of legal discipline on domestic governance. Since Brexit, that framework has been dismantled — and what is being built in its place deserves far more scrutiny than it has received.

The constitutional consequences of leaving the EU are rarely the subject of front-page debate. They lack the visceral immediacy of rising food prices or crumbling hospital waiting lists. Yet the legal reforms set in motion since 2016 may ultimately prove more consequential than any single economic statistic. They concern nothing less than the distribution of power within the British state.

The Retained EU Law Question

When Britain left the EU, it inherited an enormous body of legislation — some 4,000 pieces of retained EU law — that had been incorporated into domestic law through the European Union (Withdrawal) Act 2018. The question of what to do with this inheritance became one of the most contested legal debates of the post-Brexit era.

The Retained EU Law (Revocation and Reform) Act 2023 represented the government's answer, albeit a significantly amended one. In its original form, the Bill proposed a sweeping 'sunset clause' under which vast swathes of retained EU law would automatically expire unless actively preserved. Critics — including senior lawyers, parliamentary committees, and industry bodies — warned that the sheer volume of legislation at risk made proper scrutiny impossible. The government eventually retreated from the most radical version of the proposal, but the episode illuminated a deeper tension: the desire to signal a clean break with EU legal norms was colliding with the practical reality that much of that law underpins everyday life, from workplace rights to food safety standards.

What emerged from the process was not a coherent legal settlement but a patchwork — some EU-derived protections preserved, others quietly dropped, and the overall picture obscured by the complexity of the legislative process itself. For a constitutional order that prizes parliamentary scrutiny, this was a troubling precedent.

Judicial Review and the Limits of Oversight

The relationship between the executive and the judiciary has also shifted in ways that warrant careful attention. The Judicial Review and Courts Act 2022 introduced reforms that, while presented as technical adjustments, carry significant implications for the ability of citizens and organisations to challenge government decisions in court.

The Act curtailed the retrospective effect of certain quashing orders, limiting the circumstances under which courts can strike down unlawful government action with full retrospective force. Supporters argued this provided greater certainty for public bodies; critics, including the Law Society and several senior judges, warned it weakened one of the primary mechanisms through which executive overreach is checked.

This reform did not emerge in isolation. It followed a period of acute tension between the government and the judiciary, most notably the Supreme Court's unanimous ruling in Miller II (2019), which found the prorogation of Parliament unlawful. That judgment was constitutional history in the making — and it plainly unsettled those in government who had hoped prorogation would pass unchallenged. The subsequent appetite for judicial review reform was, in part, a response to the courts' willingness to assert their constitutional role at a moment of political crisis.

Treaty-Making and the Democratic Deficit

Brexit was justified, in significant measure, by the argument that it would return democratic control to Westminster. The irony is that one area where executive power has been substantially expanded — rather than checked — is the making of international treaties.

Under the Constitutional Reform and Governance Act 2010, Parliament has a limited role in scrutinising treaties: it may resolve against ratification, but the government retains considerable latitude. As Britain has pursued an ambitious programme of post-Brexit trade agreements, from the Comprehensive and Progressive Agreement for Trans-Pacific Partnership to bilateral deals with Australia and New Zealand, the adequacy of parliamentary oversight has come under sustained criticism.

The International Agreements Committee of the House of Lords has repeatedly raised concerns about the pace and opacity of treaty scrutiny. Trade deals that affect agriculture, intellectual property, and public procurement are being concluded with a degree of parliamentary engagement that many constitutional scholars regard as insufficient. The rhetoric of 'taking back control' has not, in practice, translated into robust mechanisms for democratic accountability over the new generation of agreements struck in Britain's name.

The Devolution Dimension

The constitutional disruption extends beyond Westminster. The relationship between the UK government and the devolved administrations of Scotland, Wales, and Northern Ireland has been profoundly complicated by Brexit, and the legal dimension of that complication is frequently underappreciated.

The Internal Market Act 2020 was introduced to ensure the free flow of goods and services across the UK after the end of the EU single market's disciplining effect. But it did so by establishing UK-wide market access principles that, in the view of the Scottish and Welsh governments, overrode devolved competencies without adequate consent. The Act passed despite opposition from Holyrood and the Senedd, and it contained provisions — subsequently amended but not forgotten — that explicitly acknowledged their potential incompatibility with international law.

The precedent set by that episode — that Westminster would legislate across devolved competencies when it judged the national interest to require it — has heightened tensions within the union and raised questions about the legal underpinnings of devolution itself.

A Constitution Under Pressure

Britain's uncodified constitution has always relied on restraint and convention as much as law. Ministers are expected to act within the spirit of constitutional norms; the judiciary is trusted to exercise its role without fear of political reprisal; Parliament is assumed to scrutinise legislation with genuine rigour. These assumptions have been tested severely in the post-Brexit period.

None of this is to suggest that constitutional reform is inherently illegitimate, or that every change introduced since 2016 has been malign. Some of the retained EU law that has been revised or removed was, by any reasonable assessment, in need of updating. Judicial review reform was debated long before Brexit entered the political lexicon. And the need for a coherent internal market framework was a genuine post-Brexit challenge.

But the cumulative effect of these changes — conducted at speed, often with limited parliamentary time, and against a backdrop of executive frustration with legal constraints — deserves sustained public attention. Constitutions, even unwritten ones, are not simply technical instruments. They are the architecture of democratic accountability. When that architecture is altered piecemeal, under pressure, and without broad consensus, the risks are not merely legal. They are political, and they are long-term.

Brexit promised to restore sovereignty to the British people through their elected Parliament. Whether the legal revolution it has triggered has delivered on that promise — or quietly concentrated power in ways its advocates never publicly acknowledged — is a question that Britain's democracy has yet to fully reckon with.